The breakdown of polymer-based restorative materials is often due to a combination of chemical and physical stresses that cause wear. Presently, the most reliable predictor of clinical wear behavior is the well-planned clinical study. Although it is possible in some cases to correlate the results of such studies with an in-vitro test, such correlations do not always provide a sound scientific basis for predicting wear. It is believed that fatigue induced wear is an important phenomenon in the degradation of some restorative materials, particularly the "microfilled" composites, when used in a stress-bearing situation. This is relatively neglected area of restorative materials research. Several novel approaches will be employed in this study in order to arrive at an understanding of fatigue-induced wear of polymer materials used in restorative dentistry. A series of resin materials similar to those presently used as matrix resins for dental composites will be prepared by an industrial contractor. Some samples will be filled with low amounts of silanated colloidal silica, as is done in practice to control the viscosity of matrix materials. All samples will be characterized with respect to degree of cure and Tg. Pin- on-disc wear testing will utilize an appropriate stylus geometry to induce subsurface fatigue wear. Dynamic tensile and shear fatigue testing will be done following relevant ASTM specifications. Employing the properties thus measured, finite element modeling techniques will be used to mimic pin-on- disc wear behavior. Finally, fatigue fracture surfaces, wear surfaces, and wear debris will be characterized using classical and fractal geometric methods.